1. Field of the Invention
The present invention relates to an image generating apparatus that generates an image of a plurality of target objects existing in a virtual three-dimensional space and the like, and more particularly, to drawing contour lines in a case where target objects, in which contour lines are to be drawn, among the plurality of target objects are overlapped with one another.
2. Description of the Related Art
In video games, owing to recent improvement of process capabilities of game devices, very realistic images can be drawn in three-dimensional computer graphics. However, in a game having a specific content, when the image is too realistic, the fun of the game decreases. Accordingly, in such a case, images of a cartoon style or an animation style are drawn in the three-dimensional computer graphics by using a technique called tuned rendering. A contour line is drawn in the contour of an object (hereinafter, referred to as a tuned object) for which a tuned rendering process is performed.
Here, when the thickness of the added contour line is too thin, compared to the size of the tuned object, the contour line is not visually distinguished on the whole, and accordingly, representation of tune is deteriorated. On the other hand, when the thickness of the added contour line is too thick, compared to the size of the tuned object, only the two-dimensional contour line is visually distinguished, and thereby representation of three-dimensional computer graphics is deteriorated. Accordingly, generally, it is configured that a thick contour line is set for a large tuned object and a thin contour line is set for a small tuned object.
In addition, when there is a plurality of tuned objects in the virtual three-dimensional space, there is a case that a plurality of tuned objects are overlapped with one another in an image generated by a perspective transformation process. In such a case, in a case where the thicknesses of contour lines of the tuned objects overlapped with each other are extremely different, when the contour lines are drawn in the objects in their original thicknesses, contour lines drawn in contours which are detected in the boundary of the overlapped part become unnatural.
In particular, a feeling of strangeness is acquired from the thickness of a tuned object located on the front side (a side close to the viewing point of the virtual camera), and thus there is a case where an image in which a tuned object originally located on the inner side (a side far from the viewing point of the virtual camera) is felt to be lifted up is generated. Accordingly, an image generating system in which, in the contour detected in the boundary of the overlapped part of the plurality of tuned objects, a contour line is drawn for the tuned object located close to the viewing point and a contour line is not drawn for the tuned object located far from the viewing point has been disclosed (for example, see JP-A-2007-26111 (paragraph 0057)).
However, according to JP-A-2007-26111, in the boundary of the overlapped part, a contour line is drawn only for the tuned object located on the side close to the viewing point, and a contour line is not drawn for the tuned object located on the side far from the viewing point. Accordingly, there is a case where the contour of the tuned object located on the side far from the viewing point becomes indistinct. In addition, for example, in a case where the color of a contour line is set to a color completely different that of the main body, based on the color of the main body of the tuned object, when the color of the contour line of the tuned object located on the side close to the viewing point is close to that of the main body of the tuned object located on the side far from the viewing point, there is a problem that the contours of both the tuned objects become almost invisible.